Self adjusting sheet gripping apparatus

Abstract: An apparatus for gripping a sheet (25) includes a first gripping member (87) and a second gripping member (89), one or both of which are equipped with one or more inflatable self adjusting gripper pads or tubes (100). The inflatable gripper pad provides a more efficient, reliable and cost effective method for the first gripping member and the second gripping member to cooperate together so as to releasably grip a sheet in a printing or copying machine. A spring (95) and cam following system may be used to move the first gripping member in relation to the second gripping member. A mechanical or electromechanical pump may be used to inflate and deflate the inflatable gripper pads so as to provide the gripping action on the sheet or so as to vary the gripping pressure created by a spring and cam system. The self adjusting inflatable gripper pads of the present invention permit a uniform force distribution or pressure to be applied along the entire length of the sheet grasping nip formed by the first gripping member and the second gripping member.

Description: The present invention relates generally to an apparatus for gripping a sheet and, more particularly, concerns a self adjusting inflatable member for gripping the leading edge of a sheet so that it may be pulled through the sheet path of a copying or printing machine. Sheet grippers of various designs are commonly used in copying and printing machines, and most frequently operate by gripping the leading edge of a sheet as it is transported through the machine. The sheet gripper must reliably and readily access the sheet, and must maintain a firm grip without slippage on the sheet throughout the entire processing and transport cycle. Once the sheet has been fully processed through the sheet gripper station, the sheet is released and the sheet gripper prepares to accept and transport the next sheet. Multicolor copiers and printers often employ a gripper assembly having a set of jaws to pull a sheet along a track for the multiple pass cycles utilized to complete the copy or print. Present gripper assemblies commonly employ two jaws that grasp the sheet; one or more springs generally provide the requisite sheet gripping force. The opening and closing of the jaws may be actuated by one or more cam lifters positioned around the sheet movement track or by similar means. A uniform gripping force or pressure should desirably be maintained along the entire nip (the points where the gripper assembly jaws meet the sheet being gripped), to prevent the sheet from shifting between the jaws of the sheet gripper as it is transported. Any failure by the jaws to maintain a firm hold on the sheet can cause machine jamming or failure, or may result in inferior print and image quality. Sheet transport failures can originate from a wide variety of sources, to include operating conditions, manufacturing tolerances and others. The onset of even minor slippage or skew in the sheet will cause highly visible misregistration of the different colors in a multiple pass color system, and can cause a variety of other undesirable consequences in single or multiple pass copier and printer systems. Sheet grippers may also fail as a result of equipment wear and tear, operating environment variances, material handling situations and other causes. Further, a significant percentage of sheet grippers of known designs may be produced only to be rejected for failing to meet a relatively strict set of manufacturing tolerances that must be adhered to. At present, machining of the jaws of such sheet grippers is necessary to achieve the requisite sheet gripper performance, resulting in higher production costs, metal waste caused by milling and higher production error rates, and a weakened gripper assembly structure as a result of the necessary reshaping of the metal parts. Various approaches have been employed for gripping a sheet to be transported in a copying or printing machine, including the following. US-A-4,155,305 discloses a bending resistant gripper carriage structure for use in offset printing machines that includes an impact strip. The gripper carriage includes a fiber sandwich construction, intended to resist deformation resulting from the speed of operation and the various forces acting on such gripper carriages. US-A-5,128,726 discloses a sheet gripper that includes a silicon or like coating on an inner (gripping) surface of a sheet gripper jaw. US-A-4,629,176 discloses a paper gripper that includes upper and lower portions made from extruded aluminium for providing stiffness to the gripper assembly, and a set of spring clips for biasing the upper and lower portions in a closed position. In accordance with one aspect of the present invention, there is provided an apparatus for releasably gripping an edge of a sheet, comprising a gripping member having opposed surfaces movable relative to one another to secure and release the edge of the sheet, and characterized by fluid pressurized means, operatively associated with said gripping member, for applying a substantially uniformly distributed force along the edge of the sheet in response to the sheet being secured by said gripping member. Other aspects of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which: Figure 1 is a schematic elevational view of the gripping portions of the sheet gripper of the sheet transport system used in an electrophotographic printing machine, with the sheet gripper in the open position and further showing a sheet within the gripping nip; Figure 2 is a schematic elevational view of the gripping portions of the sheet gripper of the sheet transport system used in an electrophotographic printing machine, with the sheet gripper in the closed position and further showing a sheet secured within the sheet gripper; Figure 3 is a perspective view of the lower gripping portion of the gripping member; Figure 4 is an enlarged sectional, elevational view along the line 4-4 of Figure 3 in the direction of the arrows of another embodiment of a lower gripping portion; Figure 5 is an enlarged sectional, elevational view along the line 4-4 of Figure 3 in the direction of the arrows of a further embodiment of a lower gripping portion; Figure 6 is a side elevational view, partially in section, of the gripping portions of another embodiment of the sheet gripper in the open position; Figure 7 is a side elevational view, partially in section, of the gripping portions of the sheet gripper shown in the closed position and further showing a sheet being grasped by the sheet gripper; Figure 8 is a side elevational view, partially in section, of a fluid inflatable gripping portion of a sheet gripper in an open position; Figure 9 is a side elevational view, partially in section, of a fluid inflatable gripping portion of a sheet gripper in a closed position and further showing a sheet being grasped by the sheet gripper; Figure 10A is a perspective view of a fluid activated gripper pad as shown in Figures 8 and 9; Figure 10B is a partial side sectional, elevational view of a gripper pad in the open position; Figure 10C is a partial side sectional, elevational view of a fluid inflatable gripping pad as shown in Figures 9, 10A and 10B; Figure 11 is a side elevational view, partially in section, of the gripping portions of another embodiment of the sheet gripper used in a sheet transport apparatus with the sheet gripper shown in the open position and further showing a sheet positioned within the sheet gripper; Figure 12 is a side elevational view, partially in section, of the gripping portions of still another embodiment of the sheet gripper used in a sheet transport apparatus with the sheet gripper shown in the closed position and further showing a sheet positioned within the sheet gripper; Figure 13 is a schematic elevational view showing details of a sheet transport system used in electrophotographic printing; Figure 14 is a schematic planar view showing the sheet gripper of the sheet transport system of Figure 13; Figure 15 is a sectional elevational view, taken along the lines 15-15 in Figure 14 in the direction of the arrows, of the opposed side marginal regions of a sheet gripper; Figure 16 is a theoretical illustration of "nodal" or point gripping forces present along the nip of an upper jaw of a conventional sheet gripper; and Figure 17 is a graph showing a theoretical representation of the gripping forces present on an upper jaw of a sheet gripper (1ft-lb = 1.3558Nm); For a general understanding of the features of the present invention, reference is made to the drawings. In the drawings, like references have been used throughout to designate identical elements. It will become evident from the following discussion that the present invention and the various embodiments set forth herein are suited for use in a wide variety of printing and copying systems, and are not necessarily limited in its-application to the particular systems shown herein. Figure 13 shows sheet gripper 84 of a sheet transport 48 for transporting a sheet 25 in the direction of arrow 62 in a recirculating path of movement. A toner image developed on a photoconductive belt 20 moving in direction 22 is transferred to sheet 25 when the sheet passes through transfer zone 64. Figure 14 shows sheet gripper 84 suspended between two spaced apart timing belts 54. Figure 15 shows a sectional elevational view, taken along the lines 15-15 in Figure 14 in the direction of the arrows, of the opposed side marginal regions of sheet gripper 84. Referring to Figures 13-15, timing belts 54 are mounted on rollers 50 and 52. Belts 54 define a continuous path of movement of sheet gripper 84. A motor 86 is coupled to roller 52 by a drive belt 88. Sheet gripper 84 includes a pair of guide members 85. A pair of spaced apart and continuous tracks 55 are respectively positioned substantially adjacent belts 54. Tracks 55 are respectively defined by a pair of track supports 57. Each of guide members 85 are slidably positioned within a respective track 55. As shown in Figure 14, belts 54 are respectively connected to gripper supports 73 and 75 by a pair of pins 83. The belts are connected to the sheet gripper behind the leading edge of sheet 25 relative to the forward direction of movement of belts 54, as indicated by arrow 62 (Figure 13), when sheet 25 is being transported by sheet transport 48. The sheet gripper is driven by the belts at the locations where the sheet gripper and the belts are connected. Sheet gripper 84 further includes an upper gripping portion 87 and a lower gripping portion 89 which are biased toward each other by a plurality of springs, each being generally indicated by the reference numeral 95 (see Figures 14 and 15). Gripping portions 87 and 89 are respectively connected to a pair of gripper supports 73 and 75 as shown in Figures 14 and 15. A plurality of securing pins 97 are respectively positioned within apertures 99 of upper gripping portion 87 and secured thereto to hold springs 95 in place so as to bias upper gripping portion 87 toward lower gripping portion 89. The sheet gripper may further include a pair of cam followers (not shown) which are attached to the opposed side marginal regions of upper gripping portion 87 and function with a pair of cams (not shown) to open and close the gripping portions at predetermined intervals. Figure 16 is a theoretical illustration of a set of "nodal" or point gripping forces that might be present at any particular point along the nip of the upper gripper portion of a conventional sheet gripper The graph of Figure 17 provides a theoretical representation of the nodal gripping forces as they might exist along an upper gripper portion shown in Figure 16. The five peaks of the graph in Figure 17 correspond to the five force arrows on Figure 16, as might be present when a set of five gripper springs is used in a sheet gripper assembly. Figure 17 demonstrates that as expected, the highest nodal point forces as would be found at the location of five gripper springs along the nip of a sheet gripper, and that distortion and point loading along a gripper nip will result in nonuniform pressure along that nip. A self adjusting system, such as the fluid filled gripper pad(s) of the present invention will provide a uniform pressure along the entire nip of a gripper assembly, resulting in a more reliable assembly. Deformation of the gripper assembly jaws, point spring loading (as shown in Figures 16 and 17) and a variety of other manufacturing and operational wear conditions can lead to sheet gripper assembly failures that can be achieved with the present invention If a uniform pressure along the nip can be achieved (as would be represented by a horizontal pressure line, in contrast to the uneven force distribution shown by Figure 17), gripper assembly reliability and performance can be enhanced, and production costs can be significantly reduced. Achieving this desired uniform pressure along the nip can also reduce the total spring or other gripping force required at the nip, further reducing machine wear and costs. As such, the benefits of achieving a uniform pressure along the entire nip using a durable, self adjusting system include improved assembly life, less stringent sheet gripper manufacturing tolerances, and other important cost reductions and reliability improvements over known sheet grippers. Figures 1 and 2 are two embodiments of the sheet gripper of the present invention, generally positioned is sheet gripper assembly 84 as is shown in Figures 13 and 14. As a point of reference, Figures 1 and 2 show a partial cross section of an embodiment of the present invention enlarged 5 or more times over known sheet grippers employed in single and multipass copying and printing machines. One can thus appreciate the need for the fine parts of known grippers to be precisely machined yet extremely durable. Figure 1 shows the orientation of upper gripping portion 87 relative to lower gripping portion 89 in sheet gripper 84 when cam follower 93 is actuated to overcome the bias of springs 95. Figure 2 shows the orientation of upper gripping portion 87 relative to lower gripping portion 89 when cam follower 93 is moved to a nonactuated position. Cam follower 93 (and the cam follower at the opposite end of the gripper assembly, not shown) is in this position when they are not in contact with the cams. When gripper assembly 84 is in the closed position, upper gripping portion 87 cooperates with lower gripping portion 89 to grasp and securely hold the leading edge of sheet 25. The area at which the gripping portions 87 and 89 grasp sheet 25 defines a gripping nip, generally indicated by the reference numeral 91 (see Figures 14 and 2). Positioned upon lower gripping portion 89, near gripping nip 91, is a fluid filled gripper pad 100 (see Figures 1-2). With fluid filled elastomeric gripper pad 100 positioned as set forth above, a self adjusting uniform pressure is applied on sheet 25 between the gripping portions. As with other embodiments of the present invention shown and described herein, the gripper pads may be pre-pressurized with fluid prior to installation, or pressurized after installation in the copier or printing machine. The embodiment of Figures 1 and 2 may be mounted in the same manner as sheet gripper 84 as shown in Figure 14. Figure 3 shows a partial perspective view of further details of a lower gripping portion 89. More specifically, the lower gripping portion includes a central core 111, preferably comprised of steel sheet metal, as self adjusting gripper pad 100 can eliminate the need to machine upper and lower gripper portions 87 and 89 to the precise tolerances required with known gripper assemblies. As such, central core 111 and other parts of the gripper assembly may be formed using metal stamping or other less costly material forming methods, so as to eliminate the costs of machining. Due to the self-adjusting nature of the inflated/pressurized gripper pads, manufacturing tolerances of many of the components to various embodiments of the gripper assembly may be relaxed, resulting in lower costs, less waste and more durable sheet grippers. Increased structural strength of the gripper assembly may also result from the use of unmachined metal. Lower gripping portion 89 may further include a cast substance 113 secured to central core 111. The cast substance is cast into a desired shape on opposite end portions of central core 111 and is thus secured thereto as shown in Figure 3. The fluid filled gripper pad 100 is positioned on the sheet contact side of cast substance 113 (see Figures 1-3). Another fluid filled gripper pad (not shown) may be mounted on upper gripper portion 87, opposite gripper pad 100 on lower gripper portion 89. A pressure valve or pump (not shown) may be used to vary the internal pressure of gripper pad 100, and can thereby vary the pressure on the edge of sheet 25 as it is gripped between gripping portions 87 and 89. Figure 4 shows another embodiment of a gripper pad as may be used on a lower gripping portion 89. Gripper pad 110 is shown with sheet contact surface 112 and fluid chamber 114. Gripper pad 110 is attached in dovetail fashion to lower gripper portion 89, with locking portion 116 of gripper pad 112 inserted into locking channel 118 of lower gripper portion 89. Figure 5 shows another embodiment of a gripper pad 120 of a sheet contact surface 122 of gripper pad 120 provided a wider gripping surface so as to maintain enhanced and well distributed pressure on an adjacent sheet. An elongated fluid chamber 124 provides the desired self adjusting dispersion of pressure as applied by contact surface 122 on an adjacent sheet. Flared base 126 of gripper pad 120 interlocks with channel 128 of lower gripper portion 89 to insure gripper pad 120 remains in position. Flared base 126 may include a rigid stiffener to prevent gripper pad 120 from becoming dislodged from channel 128. Figures 6 and 7 show another embodiment of the present invention. Figure 6 shows the orientation of upper gripping portion 87 relative to lower gripping portion 89 when the cam followers are moved to a nonactuated (closed jaw) position. Figure 7 shows the orientation of upper gripping portion 87 relative to lower gripping portion 89 when the cam followers are moved to an actuated (open jaw) position. Fluid filled elastomeric gripper pad 200 positioned along lower gripping portion 89, having an outwardly biased sheet contact surface 201. When upper gripping portion 87 and lower gripping portion 89 are in the closed position as shown in Figure 7, outwardly biased sheet contact surface 201 of fluid filled elastomeric gripper pad 200 is compressed by the biasing force of springs 95, thereby insuring a uniform pressure and firm frictional grip on sheet 25. In both Figures 6 and 7, chamber 202 maintains the fluid inside gripper pad 200; lower surface 203 of gripper pad 200 is affixed by any number of means (adhesive, heat seal and/or tongue and grove as shown in Figures 4 and 5) so as to remain in position on gripper pad mounting surface 204 of lower gripping portion 89. While certain aspects of sheet gripper 84 as shown in Figures 1-7 have not been described in detail, it will be understood that the upper gripping portion 87 may be equipped with a gripper pad in a manner similar to that of lower gripping portion 89 as shown in Figures 1-7 including the use of similar materials thereto, to insure a firm frictional grip and uniform nip pressure on sheet 25. Likewise, such an upper portion gripper pad may be used in place of, or and in addition to, the gripper pads shown in Figures 1-7. Referring now to Figures 8-12, alternative embodiments to the sheet grippers shown and described in conjunction with Figures 1-7 are shown. Sheet gripper 184 may be substituted for sheet gripper 84 as shown in Figures 13 and 14 to thereby depict an alternative embodiment of the present invention. Figures 8, 9 and 10A through 10C show an expandable gripper pad 250, capable of being inflated and deflated so as to selectively permit sheet gripper 184 to grasp and release sheet 25. Figure 8 shows sheet gripper 184 in an actuated (open jaw) position, in which expandable gripper pad 250 is deflated so as to accept sheet 25 on opening 251. Figure 9 shows sheet gripper 184 in an nonactuated (closed jaw) position, in which expandable gripper pad 250 is inflated so as to grasp sheet 25 on opening 251. As shown in Figures 8 and 9, expandable gripper pad 250 rests on base 254; as fluid is moved into and out of internal cavity 253 of pad 250 by electric pump unit 258 through tube 256, upper surface 252 is selectively moved in relation to plate 262. Pump unit 258 may be an electromechanical unit actuated by electronic timing or switching means, in which the electrical current required to deflate expandable gripper pad 250 is supplied only at the point or points in which sheet gripper 184 is to release its grip on sheet 25. In this manner, sheet gripper 184 grasps sheet 25 between plate 262 and upper surface 252 of expandable gripper pad 250 when internal cavity 253 is inflated with an increased volume of fluid, as shown in Figures 9 and 10C. Conversely, when a volume of fluid is removed from internal cavity 253, upper surface 252 of expandable gripper pad 250 is displaced from its gripping position on sheet 25 (as shown in Figures 8 and 10B). Alternatively, a mechanical pump may be used, so that expansion of gripper pad 250 may be achieved by a cam system in a manner similar to that shown and described in association with sheet gripper 284 in Figures 11 and 12. Figure 10A shows a perspective view of expandable gripper pad 250 alone. Figure 10B shows an enlarged view of expandable gripper pad 250 in a deflated mode, so as to permit the release of sheet 25. Figure 10C shows expandable gripper pad 250 in an inflated mode, so as to permit sheet gripper 184 to grasp sheet 25 between plate 262 and expandable gripper pad 250. Figures 11 and 12 show an alternative embodiment (sheet gripper 284) to the sheet gripper embodiments 84 and 184 as shown in other Figures hereto. The elastomeric gripper contact surface 302 shown in Figures 11 and 12 is capable of being inflated and deflated so as to permit sheet gripper 284 grasp and release sheet 25. Figure 11 shows sheet gripper 284 in which elastomeric gripper contact surface 302 is deflated, so as to permit slot 300 to accept sheet 25. Figure 12 shows sheet gripper 284 in which elastomeric gripper contact surface 302 is inflated, so as to permit slot 300 to grasp sheet 25. Figure 11 shows sheet gripper 284 in an actuated (open jaw) position; as wall 306 of fluid bladder 304 is raised by the actuation of cam lever 309, gripper contact surface 302 is deflated according to the outward movent of wall 306 so as to permit sheet gripper 284 to accept sheet 25. In this manner, as one wall of fluid bladder 304 is mechanically manipulated, due to the constant internal volume of fluid bladder 304, gripper contact surface 302 is drawn inward so as to open slot 300. Wall 306 is normally biased by spring 308 in lowered position (as shown in Figure 12). As cam lever 309 is permitted to drop into nonactuated position as shown in Figure 12, gripper contact surface 302 is expanded outward, closing slot 300 so as to permit sheet gripper 284 to grip sheet 25. Cam lever 309 thereby selectively pressurizes and depressurizes the fluid in bladder 304, resulting the application of uniform pressure along the entire nip by gripper contact surface 302.

Claims: An apparatus for releasably gripping an edge of a sheet (25), comprising: a gripping member (84) having opposed surfaces (87,89) movable relative to one another to secure and release the edge of the sheet; and characterized by fluid pressurized means (100), operatively associated with said gripping member, for applying a substantially uniformly distributed force along the edge of the sheet in response to the sheet being secured by said gripping member. The apparatus of claim 1, wherein said fluid pressurized means (100) comprises a resilient gripper pad secured to one (89) of the surfaces of said gripping member. The apparatus of claim 2, wherein said gripper pad (100) is inflatable. The apparatus of claim 3 wherein said inflatable gripper pad (100) is filled with a fluid selected from the group consisting of a gas, a liquid, a gel, and a fluidized foam. The apparatus of claim 3, further comprising a sealed gripper tube secured to the other surface of said gripping member, said gripper tube being filled with a fluid selected from the group consisting of a gas, a liquid, a gel and a fluidized foam, wherein said inflatable gripper tube cooperates with said inflatable gripper pad to grip the edge of the sheet. The apparatus of claim 3, further comprising means for varying internal pressure of said inflatable gripper pad so as to alter the forces on the sheet being secured by said gripping member. The apparatus of claim 3, wherein said inflatable gripper pad (250) comprises: a gripper wall (252) opposite the other surface said gripping member; and a pump (258), associated with said inflatable gripper pad, for releasably inserting a volume of fluid into the inflatable gripper pad to move said gripper wall so as to releasably grip the edge of the sheet. The apparatus of claim 3, wherein said inflatable gripper pad comprises: a sheet gripper contact surface (302) positioned opposite to and movable in relation to the other surface of said gripper member; and a volume displacing wall (306) capable of moving the fluid in said inflatable gripper pad to move said sheet gripper contact surface in relation to the other surface of said gripping member so as to releasably grip the edge of the sheet. The apparatus of claim 3, further comprising: a cam (309); and a fluid bladder (304), actuated by said cam, to vary pressure inside said inflatable gripper pad, whereby a a sheet gripper contact surface (302) of said inflatable gripper pad is moved in relation to the other surface of said gripping member so as to releasably grip the edge of the sheet. The apparatus of claim 3, further comprising an electric pump, associated with said inflatable gripping pad, to vary pressure inside the inflatable gripper pad, whereby a a sheet gripper contact surface (302) of said inflatable gripper pad is moved in relation to the other surface of said gripping member so as to releasably grip the edge of the sheet.

Inventors: REDDY KARIMIREDDY HARI, REDDY, KARIMIREDDY HARI
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1994
Main classification: B65H5
IPC codes: G03G15, B65H5, B65H29